 Abstract | Gibbsite scale growth in pipe fittings is a major problem for an alumina refinery. A recent
investigation into the scale growth mechanism at an alumina refinery found almost 60 % more
scale growth in a reducer when compared with the connecting straight pipe sections for similar
flow conditions.
Scale growth occurs where liquor (supersaturated solutions) come in contact with solid surfaces
and it is affected by the liquor flow velocity besides other physical and chemical parameters. The
present work is dedicated to study the hydro-dynamical aspects of the mechanism of scale
growth. In particular, the role of the phenomenon of turbulent bursting, stream wise and cross
stream fluctuating velocity components (Ux and Uy) was investigated as the flow moves through
the reducer. Particle Image Velocimetry (PIV) technique was used to get a full view of the
reducer and the readings close-to-the-wall of the reducer at Reynolds number of 27,000 and
44,000 upstream which corresponds to Reynolds number of 41,500 and 66,000 downstream of
the reducer respectively.
The results showed an increase in cross stream and a decrease in magnitude of stream wise
fluctuating velocity components, whereby we presume that the increased cross stream fluctuating
velocity component increases the frequency of impacts of the scaling particles on the wall thus
initiating excessive scale growth in the reducer when compared with the connecting straight pipe
sections, for similar flow conditions. |
